Crystal structure of the cubic double-perovskite Sr2Cr0.84Ni0.09Os1.07O6

The crystal structure of the cubic double-perovskite Sr2Cr0.82Ni0.11Os1.07O6 at 113 K is reported. The refined structure shows that this cubic form is stable at 113 K.


Chemical context
Recently, so called double-perovskites (DP) having AB 0 B 00 O 6 (A = divalent ions such as alkali earth or Pb, B 0 /B 00 = 3d/4d/5d transition metals) composition have attracted attention in the field of solid-state physics/chemistry due to their potential as materials for applications in, for example, spintronics, multiferroics, and/or magneto-caloric materials. In 1998, Sr 2 FeMoO 6 , which has the DP structure, was reported as having half-metallic behavior with a high Curie temperature (T C = 420 K) (Kobayashi et al., 1998). After this discovery, many analogous DP compounds showing half-metallic and ferrimagnetic behavior have been reported (Table 1). The main contributors to the specific physical properties are the electronic states of the B 0 and B 00 elements. As an example, Sr 2 CrOsO 6 , which shows the highest T C , has its majority-spin orbital empty while the minority-spin orbital is fully occupied. Both Cr 3+ (3d 3 , t 2g 3) and Os 5+ (5d 3 , t 2g 3) activate primarily for this state (Mandal et al., 2008). To enhance the property, we have introduced other transition metals into the B 0 and B 00 sites and examined for the exchange effects of such alternate transition metals at these sites. For this study, the samples were synthesized by high-pressure techniques; this was required to achieve the effective substitution.

Structural commentary
The crystal structure of Sr 2 Cr 0.84 Ni 0.09 Os 1.07 O 6 has cubic symmetry of space group Fm3m, having one Sr, one Os, one Cr, and one O atom on crystallographically independent sites in the asymmetric unit. It corresponds to the fully Crcontaining end-member Sr 2 CrOsO 6 and the low Ni-substituted Sr 2 Cr 0.75 Ni 0.25 OsO 6 (Chen et al., 2020), not the endmember of the Ni side of the composition, Sr 2 NiOsO 6 , which has tetragonal symmetry I4/m (Macquart et al., 2005), or the high Ni-substituted Sr 2 Cr 0.50 Ni 0.50 OsO 6 (HT: I4/m and LT: C2/m; Chen et al., 2020).

Synthesis and crystallization
A black-colored single crystal of Sr 2 Cr 0.84 Ni 0.09 Os 1.07 O 6 was obtained as a by-product of the synthesis of the polycrystalline Sr 2 Cr 1-x Ni x OsO 6 (x = 0.5). The polycrystalline product was synthesized from powders of SrO (99.9%, Strem Chemicals, Inc., USA), CrO 2 (Magtrieve, Sigma-Aldrich Co., USA), NiO (99.97%, High Purity Chemicals Co., Ltd., Japan), OsO 2 [labmade: Os powder (99.95%, Nanjing Dongrui Platinum Co., Ltd.) was heated at 673 under flowing O 2 gas, the process was repeated three times]. The thoroughly mixed powders (SrO:CrO 2 :NiO: OsO 2 :KClO 4 = 2:0.5:0.5:1:0.225 mol) were pressed into a pellet and sealed in a Pt capsule. All the processes were carried out in an Ar-filled glove box. A pressure of 6 GPa was continuously applied by a belt-type pressure apparatus (Kobe Steel, Ltd., Japan), the capsule was heated to 1873 K and held at that temperature for 1 h. The temperature was then quenched to room temperature, following which the pressure was gradually released.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. To ensure refinement stability, displacement parameters of disordered atoms on the same sites were constrained and the sums of occupancies were restrained (SHELXL commands EADP and SUMP, respectively.)

Funding information
Kobayashi et al.
Philipp et al.
Krockenberger et al. (2007) and Morrow et al. (2016)   Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )